Why data sources query existing infrastructure in Terraform - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to query an existing AWS VPC using a data source.

Terraform

data "aws_vpc" "example" {
  id = [1]
}

Drag options to blanks, or click blank then click option'

A"subnet-12345678"

B"my-vpc"

C"vpc-12345678"

D"instance-12345678"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a subnet or instance ID instead of a VPC ID.

Using the VPC name instead of the ID.

The id attribute must be the VPC ID, like "vpc-12345678", to query the existing VPC.

2fill in blank

medium

Complete the code to get the CIDR block of an existing AWS VPC using a data source.

Terraform

output "vpc_cidr" {
  value = data.aws_vpc.example.[1]
}

Drag options to blanks, or click blank then click option'

Acidr_block

Binstance_type

Csubnet_ids

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'id' instead of 'cidr_block'.

Using unrelated attributes like 'instance_type'.

The cidr_block attribute gives the IP range of the VPC.

3fill in blank

hard

Fix the error in the data source block to correctly query an existing AWS subnet by its ID.

Terraform

data "aws_subnet" "example" {
  [1] = "subnet-87654321"
}

Drag options to blanks, or click blank then click option'

Aid

Bvpc_id

Ccidr_block

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'name' instead of 'id'.

Using 'vpc_id' which is not the subnet's ID.

The correct attribute to specify the subnet ID is id.

4fill in blank

hard

Fill both blanks to query an existing AWS security group by its name and output its ID.

Terraform

data "aws_security_group" "example" {
  [1] = "my-security-group"
}

output "sg_id" {
  value = data.aws_security_group.example.[2]
}

Drag options to blanks, or click blank then click option'

Aname

Bid

Cdescription

Dvpc_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'description' or 'vpc_id' instead of 'name' or 'id'.

Mixing up the attributes for querying and output.

Use name to find the security group by name, and id to output its unique identifier.

5fill in blank

hard

Fill all three blanks to query an existing AWS EC2 instance by its ID, get its subnet ID, and output the subnet ID.

Terraform

data "aws_instance" "example" {
  [1] = "i-0abcdef1234567890"
}

output "instance_subnet" {
  value = data.aws_instance.example.[2]
}

resource "aws_security_group_rule" "allow_http" {
  type              = "ingress"
  from_port         = 80
  to_port           = 80
  protocol          = "tcp"
  security_group_id = data.aws_instance.example.[3][0]
  cidr_blocks       = ["0.0.0.0/0"]
}

Drag options to blanks, or click blank then click option'

Aid

Bsubnet_id

Cvpc_security_group_ids

Dinstance_type

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'instance_type' instead of 'id' for querying.

Using 'id' instead of 'subnet_id' for subnet output.

Using 'id' instead of 'vpc_security_group_ids' for security group IDs.

Use id to query the instance, subnet_id to get its subnet, and vpc_security_group_ids to get the security group IDs for the rule.

Practice

1. What is the main reason Terraform uses data sources to query existing infrastructure?

easy

A. To get information about resources created outside Terraform

B. To create new resources automatically

C. To delete unused resources

D. To backup infrastructure state

Solution

1. Step 1: Understand Terraform data sources purpose

   Data sources allow Terraform to read details about resources that exist but were not created by the current Terraform configuration.

2. Step 2: Identify the correct use case

   Since data sources do not create or delete resources, their main use is to fetch information about existing infrastructure.

3. Final Answer:

   To get information about resources created outside Terraform -> Option A

4. Quick Check:

   Data sources read existing resources = A [OK]

Hint: Data sources read info, they don't create or delete [OK]

Common Mistakes:

• Thinking data sources create resources
• Confusing data sources with resource blocks
• Assuming data sources manage resource lifecycle

2. Which of the following is the correct syntax to define a data source in Terraform?

easy

A. output "aws_vpc" "main" { id = "vpc-123456" }

B. resource "aws_vpc" "main" { id = "vpc-123456" }

C. data "aws_vpc" "main" { id = "vpc-123456" }

D. variable "aws_vpc" "main" { id = "vpc-123456" }

Solution

1. Step 1: Identify Terraform block types

   Terraform uses the keyword data to define data sources, resource for resources, output for outputs, and variable for input variables.

2. Step 2: Match syntax for data source

   The correct syntax for a data source starts with data, followed by the provider and resource type, then the name and configuration.

3. Final Answer:

   data "aws_vpc" "main" { id = "vpc-123456" } -> Option C

4. Quick Check:

   Data source syntax starts with 'data' = A [OK]

Hint: Data sources start with 'data' keyword, not 'resource' [OK]

Common Mistakes:

• Using 'resource' instead of 'data' for data sources
• Confusing outputs or variables with data sources
• Incorrect block structure or missing quotes

3. Given this Terraform data source snippet:

data "aws_subnet" "example" {
  filter {
    name   = "tag:Name"
    values = ["public-subnet"]
  }
}

What does data.aws_subnet.example.id return?

medium

A. Creates a new subnet with the name public-subnet

B. Throws an error because filter is invalid

C. Returns a list of all subnet IDs in the AWS account

D. The ID of the subnet tagged with Name=public-subnet

Solution

1. Step 1: Understand the data source filter

   The filter selects the subnet resource with the tag Name equal to "public-subnet".

2. Step 2: Determine the returned value

   Accessing data.aws_subnet.example.id returns the ID of the subnet matching the filter, not creating or listing all subnets.

3. Final Answer:

   The ID of the subnet tagged with Name=public-subnet -> Option D

4. Quick Check:

   Filter selects existing subnet ID = B [OK]

Hint: Filters select existing resources; data source returns their attributes [OK]

Common Mistakes:

• Thinking data source creates resources
• Assuming it returns all subnets without filter
• Misunderstanding filter syntax

4. You wrote this Terraform data source:

data "aws_security_group" "web" {
  name = "web-sg"
}

But Terraform shows an error: "name" is not a valid argument. What is the likely fix?

medium

A. Remove the block entirely; data sources can't query security groups

B. Replace name with filter block to find security group by name

C. Add id argument instead of name

D. Change data to resource

Solution

1. Step 1: Check data source argument rules

   The aws_security_group data source does not accept a direct name argument; it uses filters to find resources.

2. Step 2: Correct usage with filter block

   Use a filter block with name = "group-name" and values = ["web-sg"] to query by name.

3. Final Answer:

   Replace name with filter block to find security group by name -> Option B

4. Quick Check:

   Use filter block for querying by name = D [OK]

Hint: Use filter blocks, not direct name arguments in data sources [OK]

Common Mistakes:

• Using unsupported arguments in data sources
• Confusing resource and data source syntax
• Assuming data sources create or modify resources

5. You want to use a data source to get the latest AMI ID for Ubuntu in your region. Which approach correctly uses a data source to achieve this?

hard

A. data "aws_ami" "ubuntu" {
most_recent = true
owners = ["099720109477"]
filter {
name = "name"
values = ["ubuntu/images/hvm-ssd/ubuntu-focal-20.04-amd64-server-*"]
}
}

B. resource "aws_ami" "ubuntu" {
most_recent = true
owners = ["099720109477"]
}

C. variable "ubuntu_ami" {
default = "ami-123456"
}

D. output "ubuntu_ami" {
value = "ami-123456"
}

Solution

1. Step 1: Identify correct block type for querying existing AMI

   To get info about an existing AMI, use a data block, not resource, variable, or output.

2. Step 2: Verify data source configuration

   The aws_ami data source with most_recent = true, owners, and filter for name pattern correctly fetches the latest Ubuntu AMI ID.

3. Final Answer:

   Use a data source with most_recent, owners, and filter to get latest AMI -> Option A

4. Quick Check:

   Data source with filters fetches latest AMI = C [OK]

Hint: Use data source with filters and most_recent to get latest AMI [OK]

Common Mistakes:

• Using resource block instead of data source
• Hardcoding AMI IDs in variables or outputs
• Not filtering or specifying owners in data source